Solar cell and method for manufacturing such a solar cell

Abstract

A method ( 100; 100 a; 100 b; 100 c ) for manufacturing a solar cell from a semiconductor substrate ( 1 ) of a first conductivity type, the semiconductor substrate having a front surface ( 2 ) and a back surface ( 3 ). The method includes in a sequence: texturing ( 102 ) the front surface to create a textured front surface ( 2 a ); creating ( 103 ) by diffusion of a dopant of the first conductivity type a first conductivity-type doped layer ( 2 c ) in the textured front surface and a back surface field layer ( 4 ) of the first conductivity type in the back surface; removing ( 105; 104 a ) the first conductivity-type doped layer from the textured front surface by an etching process adapted for retaining texture of the textured front surface; creating ( 106 ) a layer of a second conductivity type ( 6 ) on the textured front surface by diffusion of a dopant of the second conductivity type into the textured front surface.

The invention claimed is: 
     
       1. A method for manufacturing a solar cell from a semiconductor substrate having a first conductivity type, a front surface and a back surface, the method comprising in a sequence:
 (a) texturing the front surface to create a textured front surface; 
 (b) creating by diffusion of a dopant of the first conductivity type a first conductivity-type doped layer in the textured front surface and a back surface field layer of the first conductivity type in the back surface; 
 (c) removing the first conductivity-type doped layer from the textured front surface by an etching process adapted for retaining texture of the textured front surface; and 
 (d) creating a layer of a second conductivity type on the textured front surface by diffusion of a dopant of the second conductivity type into the textured front surface. 
 
     
     
       2. The method according to  claim 1 , further comprising texturing the back surface to create a textured back surface. 
     
     
       3. The method according to  claim 2 , wherein creation of the back surface field layer is preceded by polishing the textured back surface of the semiconductor substrate. 
     
     
       4. The method according to  claim 1 , comprising during the diffusion of the dopant of the first conductivity type, forming of a dopant containing glassy layer on the front surface and the back surface from a precursor of the first conductivity type, the dopant containing glassy layer acting as dopant source for the semiconductor substrate. 
     
     
       5. The method according to  claim 4 , comprising removing the dopant containing glassy layer from the front surface and the back surface preceding the removal of the first conductivity-type doped layer from the textured front surface. 
     
     
       6. The method according to  claim 4 , comprising removing the dopant containing glassy layer from the front surface while removing the first conductivity-type doped layer from the textured front surface, in a single sided etching process. 
     
     
       7. The method according to  claim 6 , comprising removing the dopant containing glassy layer from the back surface after the removal of the dopant containing glassy layer from the front surface and the first conductivity-type doped layer from the textured front surface in the single sided etching process. 
     
     
       8. The method according to  claim 6 , comprising, after creating the first conductivity-type doped layer in the textured front surface and the back surface field layer of the first conductivity type in the back surface:
 (i) creating a protective layer on the back surface field layer, 
 before removal of the dopant containing glassy layer from the front surface while removing the first conductivity-type doped layer from the textured front surface in a single sided etching process. 
 
     
     
       9. The method according to  claim 8 , comprising, after the removal of the dopant containing glassy layer from the front surface while removing the first conductivity-type doped layer from the textured front surface in a single sided etching process and preceding the creation of the layer of the second conductivity type on the textured front surface:
 (i) removing the protective layer and the dopant containing glassy layer from the back surface 
 
     
     
       10. The method according to  claim 4 , comprising, preceding the removal of the first conductivity-type doped layer from the textured front surface:
 (i) removing the dopant containing glassy layer from the front surface and the back surface, and 
 (ii) creating a protective layer on the back surface field layer. 
 
     
     
       11. The method according to  claim 10 , wherein the protective layer comprises a coating layer containing at least one material selected from a group of aluminum oxide (Al 2 O 3 ), silicon nitride (SiN x ), a dielectric, and a resist. 
     
     
       12. The method according to  claim 1 , wherein creation of the back surface field layer by diffusion of the dopant of the first conductivity type comprises exposing the back surface to a precursor of the first conductivity type at elevated temperature. 
     
     
       13. The method according to  claim 12 , wherein the precursor of the first conductivity type contains the dopant of the first conductivity type; the precursor being selected from one of a gaseous precursor, a liquid precursor, a paste precursor and a plasma precursor. 
     
     
       14. The method according to  claim 1 , wherein the diffusion of the dopant of the first conductivity type is optimized to create a thickness of the first conductivity-type doped layer in the textured front surface of 0.7 micron or less. 
     
     
       15. The method according to  claim 1 , wherein the diffusion of the dopant of the first conductivity type is optimized to create a thickness of the first conductivity-type doped layer in the textured front surface of 0.3 micron or less. 
     
     
       16. The method according to  claim 1 , wherein creating the layer of the second conductivity type on the textured front surface by diffusion of the dopant of the second conductivity type comprises exposing the textured front surface to a precursor of the second conductivity type at elevated temperature. 
     
     
       17. The method according to  claim 16 , wherein the precursor of the second conductivity type is a gaseous precursor, the gaseous precursor containing the dopant of the second conductivity type. 
     
     
       18. The method according to  claim 1 , wherein the first conductivity type is n-type and the second conductivity type is p-type, or the first conductivity type is p-type and the second conductivity type is n-type. 
     
     
       19. The method according to  claim 1 , wherein a thickness of the first conductivity-type doped layer is less than an average height of a texture feature on the textured front surface. 
     
     
       20. The method according to  claim 19 , wherein the average height of the texture feature on the textured front surface is at least about 2 micron and the thickness of the first conductivity type doped layer is about 0.7 micron or less. 
     
     
       21. The method according to  claim 19 , wherein the average height of the texture feature on the textured front surface is at least about 2 micron and the thickness of the first conductivity type doped layer is about 0.3 micron or less. 
     
     
       22. The method according to  claim 1 , wherein the etching process adapted for retaining texture of the textured front surface is performed by a single-sided wet-chemical process using an etching agent. 
     
     
       23. The method according to  claim 22 , wherein the etching agent comprises a component for texturing a semiconductor surface. 
     
     
       24. The method according to  claim 23 , wherein the etching agent further comprises a component for polishing the semiconductor surface. 
     
     
       25. The method according to  claim 1 , wherein the etching process adapted for retaining texture of the textured front surface is performed by a dry etching method. 
     
     
       26. The method according to  claim 1 , wherein the removing of the first conductivity type doped layer from the textured front side and the dopant containing glassy layer from the front surface is performed during the etching process adapted for retaining texture of the textured front surface. 
     
     
       27. The method according to  claim 1 , further comprising partly smoothening the textured front surface. 
     
     
       28. The method according to  claim 27 , wherein the partial smoothening includes at least one of a broadening and a rounding of intermediate valleys between pyramidal shapes of the textured front surface.